docs: def build_metadata_service(did, metadata, service_endpoint):
          """
          Build a metadata service.
  
          :param did: DID, str
          :param metadata: conforming to the Metadata accepted by Ocean Protocol, dict
          :param service_endpoint: identifier of the service inside the asset DDO, str
          :return: Service
          """
          return Service(service_endpoint,
                         ServiceTypes.METADATA,
                         values={'metadata': metadata},
                         did=did)